In the next year we plan to continue our studies on the expression of the mitochondrial genome in HeLa cells. In particular, the investigation of the physical, chemical and metabolic properties of the discrete poly(a)-containing RNA species and to the individual specific tRNA species will be mapped on the HeLa mitochondrial genome by carrying out hybridization experiments with DNA fragments produced by restriction enzymes, which have been ordered with respect to known markers. The study of the functional significance of the discrete products of mitochondrial protein synthesis in HeLa cells will be continued by fractionation of the inner mitochondrial membrane into its enzymatic complexes and electrophoretic analysis of their polypeptide components. Bibliographic references: Lynch, D.C. and Attardi, G. (1975) The amino acid specificity of the tRNA species coded for by HeLa cell mitochondrial DNA. J. Mol. Biol. Submitted for publication. Mitchell, C.H., England, J.M. and Attardi, G. (1975) Isolation of chloramphenicol resistant variants from a human cell line. Somatic Cell Genetics 1: 215.